This invention relates to foam-inhibiting compositions and more particularly to organosilicon-based anti-foam compositions.
Basically, foam is a mass of bubbles created when some type of gas is dispersed into a liquid and the dispersion is then stabilized. As a result, high strength films of liquid surround the bubbles, forming large volumes of foam.
Generally, foam may be classified as desirable or undesirable. For example, the presence of foam is desirable in such industries as brewing, wine, ore flotation and fire extinguishing chemicals.
This invention, however, concerns itself with the prevention and/or destruction of undesirable foams. Undesirable foams and the problems related thereto are common, for example, in the petroleum industry, the asphalt industry, the food industry, ink industry, and the paper manufacturing industry. For example, if not properly controlled, foam can reduce equipment capacity and increase processing time and expense. Although foam can be controlled by making basic changes in a process itself, or by using mechanical defoaming equipment, chemical defoamers have proven to be the most effective and economical. By adding the chemical defoaming compositions to the system, stabilizing films are broken, causing the foam bubbles to vanish, thus completely defoaming the process.
Accordingly, many chemical compositions are known which are useful for the prevention and destruction of undesirable foams. Some of the most effective and versatile anti-foaming agents are the silicone defoamer. For example, it is well known that dimethylpolysiloxane will inhibit foam in lube oil systems. Foaming is highly detrimental in lubricants, since it reduces the quantity of oil fed to the moving parts of the apparatus being lubricated and therefore impedes proper lubrication action. It is theorized that the polydimethylsiloxane particles adhere to the bubble surfaces and break the foam.
Moreover, silicone fluids that are viscous liquids containing various dimethylpolysiloxanes and other polysiloxanes are used as antifoaming agents in bottling fruit juices and concentrating sugar; in cooking linseed oil varnishes; in dehydrating alkyd, melamine, urea, and phenol resins. Furthermore, dimethylpolysiloxane in combination with oleic acid when applied as an antifoaming agent in the preparation of penicillin results in greater separation and higher yields.
In the petroleum industry, oil well drilling fluids sometimes entrain sufficient air or gas to make them difficult to pump. Various defoamers have been used to break the foam and release the gas from the drilling fluid. Included among these defoamers are the silicones, alkylarensulfonates, castor oil, capryl alcohol, aluminum stearate and sulfonated vegetable oils.
A recently developed class of improved antifoam agents comprises dimethylpolysiloxane compositions containing untreated and/or treated fumed silica (e.g., fumed silica treated with octacyclotetrasiloxane). The general process by which these compositions are made requires that a mixture of the dimethylpolysiloxane fluid and the untreated and/or treated fumed silica filler is initially heated to about 150.degree. C in order to disperse the filler. The mixture is then homogenized under pressure or milled and cooled. The mixture is then reheated to about 150.degree. C for a considerable time to insure proper filler wet out. Finally, the mixture is again cooled and charged to a desired container for subsequent use.
Thus, as is evident from the above-described process, manufacture of this recently developed class of antifoam compositions is extremely costly and extremely time-consuming. In addition, the efficiency of the final products as defoamers has left room for considerable improvement.